Bridge circuits are frequently used in feedback control systems in order to supply an analog output proportional to the sensed condition where a steady state operation is the object of the sensing system. Other elements of the bridge are designed so that any variation away from the desired control point in the sensed condition produces an error signal at the output of the bridge. The error signal may then be converted into a digital quantity in order to take corrective action.
One of the significant problems relating to the use of bridge circuits is that the output of the bridge circuit is not only affected by changes in the sensed condition, but may also be affected by variations in the supply voltage to the bridge. In order to remedy that problem, voltage regulators have been used with bridge power supplies. While that technique does remedy the problem, it can be quite expensive if the power supply is also connected to other apparatus, that is, where the power supply has a significant load. Additionally, if regulation is to be 1 percent or less of nominal voltage value, the regulator can be quite expensive even where relatively small loads are present.
The innovative circuit of this invention supplies an answer to the above problem and therefore has for its main object the production of a digital representation of an error voltage from a bridge circuit which is insensitive to the effects of power supply variation.